Arthur is a lively, ingenious 10-year-old boy. He spends all his holidays at his beloved grandmother's house. This garden is home to a world invisible to most. Arthur has discovered a passage that allows him to explore the world of the Minimoys, a tiny people. He becomes one himself by entering this world. The Minimoys face many threats, including the invasion of the armies of Maltazard, the Minimoys' sworn enemy, who reigns over the Seides.
A lonely, dreamy little boy, Arthur becomes a reckless hero who will lead an entire people to regain their freedom. Accompanied by his friends Sélénia and Bétamèche, he embarks on a series of intense adventures.